Two patients have been recruited and admitted to the General Clinical Research Center. These patients were admitted to study their macular edema which is a common cause of visual loss associated with several ocular conditions including diabetic retinopathy and vascular occlusions. Patients with macular edema often state that vision is worse in the morning and improves throughout the course of the day. In a previous study using the General Clinical Research Center some years ago, we found the visual acuity of 3 patients with macular edema to improve over the course of a day. This was not associated with changes in refractive error and we concluded that the fluctuation in visual acuity may well have been the result of a cyclic change in the macular edema. Since the time of that original study about 1 0 years ago, instrumentation has become available that can noninvasively measure retinal thickness as an objective measure to quantitate retinal thickness and document change in macular edema. The procedure is risk free to the patient.